高炉喷吹用兰炭与煤粉非等温/等温燃烧热分析动力学研究

Thermal Analysis Kinetics of Non-isothermal/Isothermal Combustion of Char and Pulverized Coal for Blast Furnace Injection

采用热分析仪并借助等转化率的FOW(Flynn-Wall-Ozawa)方法和Malek方法(非等温燃烧)以及模式配合法(等温燃烧)比较研究了喷吹用兰炭和煤粉在非等温燃烧和等温燃烧条件下的燃烧特性、动力学参数和机理模型,其中非等温燃烧实验是在50 mL/min的空气气氛下,在升温速率分别为5℃/min,10℃/min,20℃/min条件下升温至900℃;等温燃烧实验需预先将炉腔抽成真空,随后通入Ar,在分别达到预设温度1000℃,1100℃,1200℃之后切换成空气进行反应。结果表明:非等温燃烧与等温燃烧条件下两者的燃烧反应性顺序存在显著差异,非等温燃烧条件下燃烧反应性与挥发分含量关系密切,表现为挥发分含量高的Char 1#和Coal 1#的燃烧性能较好;等温燃烧条件下兰炭粉的燃烧性能优于喷吹煤粉的燃烧性能;非等温燃烧过程的机理模型较为复杂,反应级数与扩散模型能较好地模拟燃烧动力学过程;等温燃烧过程兰炭和喷吹煤粉均以扩散为动力学模型,传质成为燃烧过程的控速环节;等温燃烧表观活化能明显小于非等温燃烧表观活化能,表明以扩散为限制性环节的等温燃烧过程更容易发生;整体上看,兰炭燃烧反应的活化能普遍低于喷吹煤粉燃烧反应的活化能。

The combustion characteristics,kinetic parameters and reaction mechanism of char and pulverized coal under non-isothermal combustion and isothermal combustion conditions were studied.The thermogravimetric analysis with Flynn-Ozawa-Wall(FOW)method,Malek method(non-isothermal)and mode fit method(isothermal combustion)was applied.Non-isothermal combustion experiment was carried out in an air atmosphere with the flow rate of 50 mL/min,the heating rate was controlled at 5℃/min,10℃/min,20℃/min,from room temperature to 900℃.For the isothermal combustion experiment,the furnace chamber was vacuumed by a vacuum pump in advance,then gas Ar was introduced.After reaching the preset temperature of 1000℃,1100℃,1200℃,the atmosphere was switched to air for reaction.The results show that there is an obvious difference in the order of combustion reactivity between nonisothermal combustion and isothermal combustion conditions.Under non-isothermal conditions,the combustion reactivity is closely related to the volatiles content.Specifically,Char 1#and Coal 1#with high volatile content have better combustion performance.However,under isothermal combustion conditions,the combustion reactivity of char is better than that of pulverized coal.The non-isothermal combustion mechanism is relatively complicated,and the combustion kinetics can be better simulated by using appropriate reaction order and gas diffusion model.For the isothermal combustion,the reaction process of both char and pulverized coal is controlled by the gas diffusion rate;namely,the mass transfer becomes the rate-determining step of the combustion process.The apparent activation energy of isothermal combustion reaction is significantly smaller than that of non-isothermal combustion,which indicates that the isothermal combustion process with gas diffusion as the limiting step is more likely to occur.Overall,the activation energy of char combustion is generally lower than that of pulverized coal combustion.